1. Field of the Invention
The present invention relates to a method for preparing nanoporous Pt/TiO2 composite particles, nanoporous Pt/TiO2 composite particles prepared by the above preparation method, and a fuel cell comprising the nanoporous Pt/TiO2 composite particles.
2. Discussion of Related Art
Fuel cells are classified into various types according to the operating temperature and the type of main fuels. The performance of a polymer electrolyte membrane fuel cell (PEMFC) and a direct methanol fuel cell (DMFC), which operate at low temperature, particularly depends on the activity of an electrode catalyst.
Platinum has been used as an electrode catalyst since the polymer electrolyte membrane fuel cell and the direct methanol fuel cell were developed. The activity of platinum is high, but it is very expensive. Therefore, extensive research aimed at increasing the utilization of platinum by highly dispersing platinum on carbon has continued to progress.
A strategy to increase the utilization of platinum is to allow platinum nanoparticles to adhere to a high surface area, porous solid support. Since the open structure of the support promotes the diffusion and absorption of reactants, the support may have an advantage as an additional catalyst. Active carbon, carbon nanotubes (CNTs), carbon nanosheets, and silica gel have been used as supports for platinum nanoparticles for use as catalysts (Kim et al., 2006; Merlo et al., 2008; Li et al., 2009; Miyatake et al., 2009; Yoo et al., 2009; Hsu et al., 2010; Winjobi et al., 2010).
Titanium dioxide powder has been widely used as a white pigment and a cosmetic composition and further used as a reaction material of barium titanate (BaTiO3), a dielectric material, and a photocatalyst. Titanium dioxide used in photocatalysis absorbs UV rays having a wavelength of 400 nm or less and excites electrons. When electrons and holes generated by excitation reach the surface of titanium dioxide particles, the electrons and holes react with oxygen or water to generate various radicals. These radicals exhibit the effect of oxidation, and thus the materials absorbed on the surface of the particles are oxidized and decomposed.
In general, the study of titanium nanoparticles is conducted to increase the surface area of nanoparticles with reduced and uniform particle size. Moreover, the study of preparing particles with a crystal phase of a desired fraction is conducted to improve the photocatalytic properties by controlling the crystal phase of the prepared particles.
Titanium dioxide nanoparticles are used as supports for improving the catalytic activity of platinum, but most of the studies relate to the synthesis of platinum/titanium dioxide complexes in which platinum is deposited on the surface of titanium dioxide.